The present invention relates to an electromagnetic inductor for generating a magnetic field with helical movement in a cylindrical volume through the superposition of a rotating magnetic flux and an axially moving magnetic flux. Such an inductor includes a first magnetic circuit comprising a core made from a stack of thin magnetic crowns, insulated one from the others, tightly held between ring-shaped end plates, and cut out on the internal side to form wide, regularly spaced teeth in the circumferential direction divided by notches, and a first polyphase induction winding having coils which are disposed in the notches to generate the rotating flux. A second magnetic circuit includes bars parallel to the axis and foliated in generally diametrical planes, and a second polyphase induction winding made up of circular coils, axially spaced and coaxial to the first magnetic circuit, in which the phases of the windings axially follow one another to generate the axially moving flux.
The utilization of a magnetic field with helical movement for the rabbling of billets in a continuous casting installation is the subject of commonly assigned U.S. patent application Ser. No. 38,428 filed May 14, 1979, now abandoned. Two possible embodiments of inductors are described in that application. A first set of coils set up in the notches of the first magnetic circuit of the inductor creates a rotating field, and a second set of circular, axially and regularly spaced coils creates an axially moving field. Yokes made up of bars, parallel to the axis and regularly spaced in the circumferential sense, permit closing of the loop of flux generated by the second set of coils.
In the two types of inductors described in the previously mentioned application, the mounting of the windings and of the elements of the magnetic circuits is difficult because the coils and the other elements of the magnetic circuits are imbricated one in the others. Furthermore, an additional problem arises in inductors where there is a coexistence of polyphase polar coils set up on the periphery of a magnetic circuit for creating a rotating magnetic field and coaxial circular coils surrounded by magnetic yokes in the shape of straight bars set up around these circular coils. Such an inductor must be designed so that the combination of fluxes generated by the two systems permits each one of the flux paths to close without a mutual reaction between the coils of one system and the yokes of the other system, in order to avoid parasitic electrical losses and to obtain the impedance of the adjustments of the two modes of action on the secondary load, due to a perfect decoupling of the magnetic circuits.